The Activation of Enzymes with Light

Abstract

Photoresponses have been described for bacteria, fungi, protozoa, algae, plants, invertebrates, and higher animals. These responses include phototaxis, phototropism, photomorphogenesis, photoperiodism, vision, and photocontrol of biological rhythms. The molecular details for the translation of a light stimulus to the observed biological response remain largely unknown for most responses to light. One possibility for the primary process in the stimulation of biological responses is the enhancement by light of an enzyme reaction. This can involve direct absorption of photons by an immediate component of the enzyme system (e.g., substrate), or indirect effects of light on enzymes such as the enhancement of protein synthesis, and enzyme activation which requires an additional protein acting as a light activation factor. The light activation of enzymes represents a topic that is developing rapidly, with particular emphasis in the areas of vision, photochromic enzyme inhibitors, photoreactivation, and enzyme activation in photosynthetic organisms. A few years ago there were not many reports on the activation of enzymes by light, whereas the photomactivation of enzymes has received widespread attention for years. Light activates specific enzymes, whereas inactivation by exposure to far-UV* radiation or by photodynamic action is not enzyme specific. Some inactivations by visible or near-UV light are selective, but are usually not reversible.

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